Let's start from the top. There are only three tools that can legitimately change an ELF file (okay maybe four but I'll go into that later): strip, chpax/paxctl, and prelink. The first is designed to remove debug information, and Portage already runs it on files before the livefs merge. The second (actually two tools, but one is the new one) is for hardened, and is not going to be deprecated in favour of using xattr marking, and the third is a way to try to reduce the overhead of running programs. For more information about the third I'll point you to my blog's tag as I've written quite enough on the subject.

In your case, the latter is what caused the change; if you compare the two files with a more simple 'readelf -S' instead of a full blown objdump, you can see that the new file has three new sections that are not present in the old one: .gnu.liblist.gnu.libstr and .gnu.prelink_undo. These three sections are where the extra space is coming from.

P.S.: the fourth tool I refer to above is chrpath, but that's only used to change the runtime search path for proprietary software, almost exclusively, so it really can't apply go glibc._________________You want to know what I'm working on right now? Just follow my blog.